3. Register if you're not self-employed
If you have to send a tax return and didn’t send one last year, you need to register for Self Assessment by 5 October.
If you’ve sent a return before
To register, you’ll need the 10-digit Unique Taxpayer Reference (UTR) from when you registered previously. You can find your UTR if you’ve lost it.
Use the online account you set up previously to file your tax return.
If you haven’t sent a return before
You’ll get a letter within 10 working days (21 if you’re abroad) which will contain your Unique Taxpayer Reference (UTR). You’ll need this to enrol for Self Assessment online services so you can file your return online.
You’ll get an activation code in the post within 10 working days of enrolling (21 if you’re abroad). You’ll need this when you first log in to your online account. You can replace an activation code if you don’t receive it or you lose it.